A variety of devices have been disclosed in the past to dissipate a beam of energy. Previous devices include energy traps, light traps, beam dumps, and the like. All of the prior art devices have suffered from one or more drawbacks that made their use and performance less than ideal or desirable under at least certain circumstances.
An energy beam (e.g., a beam of light) is useful for the interrogation of properties or constituents of a liquid sample. Examples of properties of a liquid sample which can be interrogated by a beam of light include, but are not limited to, an amount of particulate matter present in the liquid correlated to an intensity of scattered, the absorption coefficient, pH, a chemical composition, a refractive index, a concentration of a chemical constituent comprising the liquid, and a density or temperature of the liquid.
In performing testing to ascertain the foregoing properties, it is common that the liquid to be measured is in equilibrium, and/or saturated, with a gas. For instance, the liquid can be in equilibrium with air for a given temperature and pressure. As an example, the liquid is saturated with gasses present in the environmental conditions at which the liquid is measured. It is also often advantageous for the detector used for the assay (or interrogation) of a liquid to be immersed in the sample within a measurement chamber and in close proximity to an energy beam so as to minimize signal loss and/or increase the energy density at the detector. It is therefore common for a light/energy trap to be integral with the measurement chamber to absorb the portion of the beam energy propagating outside the field of view of the detector (or more specifically a photodetector wherein the energy beam comprises light). The integral nature of the light trap often precludes replacement or interchangeability as may be desired for enhanced performance or other special requirements such as the assay of caustic liquids or other liquids that exceed typical operational parameters of the as-installed trap.
Most typically, the portions of an energy beam impingent upon an energy absorbing surface in a light/energy trap immersed in a liquid are absorbed and converted into heat. Localized heating of a liquid that is at equilibrium with a gas at a given temperature and pressure will cause localized outgassing of the liquid, precipitating the formation of gas bubbles on the impingent surface. The gas bubbles on the submerged surface of the trap increase reflectivity proximate the surface by (i) creating an additional optical interface (gas-liquid interface) between the liquid and each gas bubble, and (ii) increasing the difference in the refractive indices at the surface of the energy absorbing media (a gas-surface interface).
To further deleterious effect, bubbles disposed upon the immersed surface change the scatter characteristics of the surface by increasing the roughness of the apparent surface. As a result, an energy beam incident on such a surface will scatter light with greater intensity and with less predictability than a surface without bubbles. An increase in both the amount and direction of scattered energy increases the probability that at least some of this errant energy will be received by the detector. Errant energy received by the detector mimics the presence of analyte in the liquid and limits the detection thereof.
In applications where the excitation or interrogating energy beam does not terminate incident upon a detection means, such as in a turbidity or photoluminescence assay, even a small amount of stray energy can have significant negative effects on the accuracy of an assay. In a turbidity or a photoluminescence assay, the detector is commonly positioned at a right angle to the interrogating energy beam and the emissions from the analyte of interest are extremely weak (typically more than 10,000 times weaker than the energy of the interrogating beam). The high energy of the interrogating beam relative to the weak emissions of the analyte require high amplification of the emission response of the detection means making the detection means highly susceptible to stray energy of the excitation or interrogating beam.
The construction of prior art beam dump and energy/light trap devices also require the energy absorbing surfaces be compatible with the liquid in which they are immersed so that the low reflectance surface of the energy/light trap does not degrade over time and become more reflective causing drift and error in the measurement due to stray light as previously described. As can be appreciated, this constraint limits the number of materials available to manufacture an energy/light trap.
As a further drawback, at least some prior art energy/light trap devices are constructed integral to a measurement chamber which slows the response of the measurement chamber by placing obstructions along the flow path of a liquid sample.